Abstract
This paper describes the design of current mode low-pass ladder filters based on CMOS technology. The filters are derived from passive RLC ladder filter proto- types using new CMOS lossy and lossless integrators. The all-pole and Elliptic approximations are used in the pro- posed low-pass filter realizations. The proposed two types of filter can be electronically tuned between 10 kHz and 100 MHz through bias current from 0.03 µA to 300 µA. The proposed filters use 1.5 V power supply with 3 mW power consumption at 300 µA bias current. The proposed filters are resistorless, use grounded capacitors and are suitable for further integration. The total harmonic distor- tion (THD) of the low-pass filters is less than 1% over the operating frequency range. PSPICE simulation results, obtained by using TSMC 0.18µm technology, confirm the presented theory.
Highlights
Active filters are essential building blocks in analog signal processing in communication, instrumentation and control systems
It can be seen that the all-pole low-pass ladder filter can be designed based on lossy and lossless integrators
In a similar way using the Elliptic filter signal flow graph (SFG) shown in Fig. 11(b), the third-order Elliptic low-pass ladder filter can be constructed by using lossy, lossless integrators and additional current gains
Summary
Active filters are essential building blocks in analog signal processing in communication, instrumentation and control systems. The realizations of current-mode leapfrog ladder filters using the current-difference buffer-amplifier (CDBA) and the differential-voltage current-conveyor (DVCC) were presented in [13] and [14] respectively These realizations require many active building blocks and use floating resistors and may, be not suitable for integration. It appears that there is a need for new designs of high-order LPFs enjoying the following attractive features: use of less number of active and passive components, avoid the use of resistors, enjoy the electronic tunability of the filter parameters and are suitable for integration It is the major intention of this paper to present two transistor level designs of current-mode thirdorder ladder low-pass filters using CMOS technology. The PSPICE simulation results obtained are in excellent agreement with the theoretical results and confirm that the proposed filters are suitable for high-frequency up to VHF which would be very suitable for designing communications system
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